Origin of the word "derrick". Urban legend?

In another thread they talk about how executioners wore masks either to hide their identity or to symbolize that the worked for the state. According to something I read the word derrick (as in oil derrick) comes from the name of a “famous” 16th century hangman. Is this an urban legend? If not, how did people know who he was if he wore a mask?

My Merriam-Webster Collegiate says is comes from “derrick - a hangman or gallow. After Derick a 17th century English hangman.”

From the OED {some abbreviations and fine print omitted}:

And from a now obsolete meaning of derrick as “to hang”:

So either the hangman in those days didn’t wear a mask, or the mask was just symbolic and those in the know knew his identity.

Maybe he was wearing one of those “Hi my name is Derrick” tags.

I honest to god don’t know if English hangmen wore masks in those days, though I should, given some of the odd books I’ve read. However, there’s a difference between being able to say.“The hangman’s name is Derrick”, and being able to say “Hey, there’s Derrick the hangman. Didn’t he hang both your brothers, Big 'Arry?” A mask would certainly be helpful in ensuring that the first example did not turn into the second.

Question: was Derrick a hangman?
Or, did the name Derrick appear after the term applied to hangmen, & crept into the language just like the name Smith or Jones. Derrick can be a family name, too, you know.

Was Derrick hung like a derrick?

I can’t help wondering… was his surname Diggler?